深部应力敏感裂缝性地层漏失封堵力学机理研究

在油气钻井过程中，井漏问题给石油工程界带来极大挑战，尤其在深井钻井过程中遇到应力敏感裂缝性地层时，漏失问题更加突出。利用裂缝性钢板评价封堵的传统方法无法模拟应力敏感性及真实岩心孔隙结构等特征。本项目提出开发大尺寸真三轴钻井堵漏模拟评价装置，实现接近真实环境的室内裂缝性地层的漏失封堵模拟研究，分析封堵承压结构体破坏的力学机理，解决漏失通道开启与扩展的力学问题。鉴于以上目标，只有通过对人造裂缝性岩心试样进行真三轴的漏失封堵模拟实验，并运用岩石力学、断裂力学、实验力学等理论方法进行综合研究。为此，将根据相似理论，研究室内岩心几何尺寸与真实地层、实验参数、与现场施工参数的对应关系；考虑裂缝和孔隙特征造成应力敏感行为的差异，研究堵漏材料封堵裂缝性地层的微观机理，揭示堵漏过程中裂缝性漏失通道封堵开启与扩展的力学机理，建立裂缝性漏层承压能力的时效性评价方法。本项目为现场窄密度窗口下安全钻井提供理论支撑。

In the process of oil and gas drilling, lost circulation posed great challenge to the whole industry both in technique and economic aspects. In particular, when encountered the stress sensitive and naturally fractured formation in the deep drilling process, lost circulation is more serious. Since the traditional plugging technique evaluation method with fractured plates cannot simulate the stress sensitivity and pore structure characteristics of the real core, this project proposed to develop large size true triaxial lost circulation control simulation evaluation device, in order to realize the loss circulation control simulation research close to the real situation in laboratory. Only in this way, it is possible to analyze the mechanical mechanism of the plugging confined structure failure and study the mechanism of the lost circulation path initiation and propagation in stress sensitive and naturally fractured formation. In view of the above objectives, the true triaxial loss circulation control simulation experiments will be done with artificial fractured core samples and a comprehensive study will be conducted using rock mechanics, fracture mechanics, experimental mechanics and other theoretical approaches. To this end, the corresponding relationship between the geometry of laboratory core and the true formation, experimental parameters, field operational parameters will be study based on the similarity theory. Considering the stress sensitivity difference due to fractures and pore features, microscopic mechanism of plugging material used in naturally fractured formation will be studied. Mechanical mechanism of lost circulation path initiation and propagation in stress sensitive and naturally fractured formation will be discussed and efficiency evaluation method for formation fracturing capacity will be established. The whole study can provide a theoretical basis for the realization of safe drilling under a narrow density window.